Planing machines are used in the lumber industry to plane lumber, giving different pieces of lumber specific profiles. Automatic planing machines usually include a feed table, upper and lower planing heads (also called cylinders), a linebar, and right and left side planing heads. The feed table is used for the preliminarily vertical positioning of the piece of lumber with respect to the upper and lower planing heads. The linebar is usually fixed and is used to laterally guide the piece of lumber along a travelling course in the planing machine. The side planing heads, usually right and left, are used to plane the side surfaces of the piece of lumber. They define a planing width therebetween.
The U.S. Pat. No. 6,666,246 (GILBERT) teaches an automatic planing machine which also includes an automated positioning system for improving the performance of the machine. This positioning system is provided with positioning means for adjusting the position of at least one of the planing heads and further includes position encoders for producing the position signals indicating the height of the feed table and the planing level of at least one of the planing heads. Thus, the piece of lumber and the planing levels are closely monitored and can be quickly adjusted to achieve high production rates and improved planing quality.
FIGS. 20 and 21 (PRIOR ART) represent prior art in side planing heads positioning devices for automated planing machines as taught by the above-mentioned U.S. patent. As can be appreciated in these Figures, the planing heads positioning device 30 includes a main frame 32, to which an intermediate module 34 is mounted with linear slides 36. The first planing head 38 and second planing head 40, both being side planing heads, are respectively mounted to sub-frames 41A, 41B. The intermediate module 34 can be slid and positioned with respect to the main frame and the sub-frames 41A, 41B can be positioned with respect to each other to make the planing width larger or smaller. This setup requires drive means for both sub-frames and for the intermediate module, and therefore suffers from drawbacks associated with the extra weight and complications arising therefrom.
According to U.S. Pat. No. 6,666,246, the side planing heads can be moved individually by positioning means, or simultaneously on a mobile frame, which is slidably connected to the main frame. Planing heads positioning devices are units that are usually heavy, including multiple frames and/or positioning components. In planing operations, the masses and speeds of the moving components are important factors that have a direct effect on the efficiency and durability of the system. The inertia of large or heavy components of the machine imposes certain difficulties. Heavy components are more difficult to control and handle and may increase the wear on the system. Precisely and rapidly adjusting such massive components, for example with heavy positioning means and position encoders, can pose problems.
Furthermore, for piece by piece positioning, it is important to be able to make small adjustments to the position of the planing heads in order to account for variations in the incoming raw piece of lumber. It is advantageous for a planing heads positioning device to be able to position the right and left planing heads simultaneously, thus shifting the travelling course of the piece of lumber without changing the planing width. It is also advantageous for the device to be able to position the planing heads relative to each other, thus changing the planing width defined therebetween. In the prior art, devices for positioning planing heads have comprised various assemblies. In one assembly, the planing heads (right and left) are each mounted to separate mobile frames, and the frames are slid back and forth on the main frame by pairs of screw members. In another design, two mobile frames supporting the planing heads are mounted on an intermediary module or frame, which, in turn, is mounted on the main frame and can be slid back and forth thereon. This second design enables the planing heads to be positioned simultaneously or individually, but includes three frames as well as three motorized drive means to move them. The prior art therefore teaches heavy and complicated assemblies including numerous supports and numerous drive means for positioning planing heads.
Another disadvantage of the prior art is that conventional planing machines use transmission systems with a single screw offset with respect to the axis of the side planing heads to move them. This offset makes displacement more difficult, inaccurate and increases the wear of the components. The required torque to effectuate the movement is also increased, jams are more frequent and durability of the components suffers.
There is thus a need for an improvement of planing heads positioning devices in automated planing machines, which up to now have incorporated massive and awkward components that cause various inefficiencies, component wear, complexities and other disadvantages.